DuraChimney 10″ Class A Chimney Pipe Firestop The DuraChimney II 10″ Class A Chimney Pipe Firestop is a component that is used in a typical venting installation. Use in ceiling/floor penetrations above fireplace. Firestop is not required when passing through the roof. Fits on underside of ceiling. Features: Type: Chimney Pipe Firestop. Collection: DuraChimney II. Used in Ceiling/Floor Penetrations Above Fireplace. For use with DuraChimney II 10″ Class A Chimney Pipe. Specifications: Overall Dimensions: 19.62″ (W) x 19.62″ (D). Firestop is 1″ Thick. Dimensions: 19.62″ x 19.62″.